1. Field of the Invention
The present invention relates to a tire having a coated surface, in particular a coated outer surface.
More in particular, the present invention relates to a tire comprising at least one outer structural element, said at least one outer structural element being at least partially coated by at least one coating layer including a crosslinked composition in order to modify its surface appearance, in particular in order to obtain an outer structural element having a coloured and/or a glossy surface.
2. Description of the Related Art
Compositions intended to cover the outer surface of tires, in particular coloured compositions, are already known in the art.
For example, U.S. Pat. No. 3,648,748 relates to a tire comprising a cured rubber tire having adhered thereto a laminate of a cured polyurethane comprising a cured reaction mixture prepared by reacting an organic polyisocyanate with a reactive hydrogen containing polymeric material having a molecular weight of from about 700 to about 5000 and a hydroxyl functionality greater than 2.0 up to about 3.0 selected from hydroxyl terminated polymers of the group consisting of polymer and copolymers of 1,3-diene hydrocarbons having 4 to 6 carbon atoms, copolymers of 1,3-diene hydrocarbons having 4 to 6 carbon atoms with styrene, acrylonitrile, ethyl acrylate and chloro substituted 1,3-diene hydrocarbons having 4 to 6 carbon atoms. The tire is prepared by the method which comprises (A) cleaning a portion of the surface of a cured rubber tire to be coated with a solvent, (B) coating the said surface with the liquid polyurethane reaction mixture and (C) curing the said reaction mixture to form a composite structure. The abovementioned laminate is said to be formed on the cured rubber tire without previously chemically treating the rubber and to provide a decorative, protective or identification surface for the tire.
International Patent Application WO 98/14338 relates to a method of imprinting markings on rubber articles, more particularly tires, the marking being applied by means of ink and the rubber article comprising no wax or stabilizer additives in the marking portion, characterized by the marking being imprinted (for example, by a tampon printing method) and by the ink comprising a binding agent which is adapted to the rubber blend of the marking portion. Preferably, said ink is a solvent-based two component ink comprising from 20% to 35% of coloring pigments and/or from 2% to 5% vehicle and/or from 40% to 60% solvent and/or from 15% to 20% binding agent said binding agent comprising polyurethane resin and polyurethane prepolymer. Preferably, the ink is cured with aliphatic or aromatic isocyanates. The abovementioned method is said to give good durability of the marking on the rubber article. In addition, by eliminating wax or stabilizer additives, there is no risk of the tire or marking in the marking portion becoming discolored.
United States Patent Application 2004/0050471 relates to a tire having an outer rubber surface based at least in part on essentially unsaturated diene elastomers, said outer rubber surface covered with a coloured coating bonded thereto, said colored coating having at least one layer in contact with air and including a composition comprising:    (1) a polyurethane in majority proportion; and    (2) flakes of aluminum in an amount of between 20 and 150 parts of flakes per hundred parts of dry polyurethane (phr);wherein the polyurethane is produced from a polyol selected from the group consisting of aliphatic polyethers, aliphatic polyesters, polyethers having a main chain that is semi-aromatic and polyesters having a main chain that is semi-aromatic; and the bond between the elastomer and coloured coating results from interaction of the polyurethane and polar functions on the elastomer. In fact, said composition is laid on the vulcanized tire after treatment of the tire surface to provide reactive polar functions. The above-mentioned colored coating is said to inhibit the degradation due to oxidation and ozone and greatly limits the migration of the antioxidants towards the surface of the tire, allowing the rubber composition to retain its color. Furthermore, the coating prevents the migration of the waxes towards the surface by a barrier effect, thereby avoiding efflorescence and retaining its surface appearance.
United States Patent Application 2004/0055680 relates to a tire having an outer rubber surface based at least in part on essentially unsaturated diene elastomers, said outer rubber surface covered with a coloured coating bonded thereto, said coloured coating having at least one layer in contact with air and including a composition comprising:    (1) a polyurethane in majority proportion; and    (2) flakes of mica in an amount of between 10 and 80 parts of flakes per hundred parts of dry polyurethane (phr);wherein the polyurethane is produced from a polyol selected from the group consisting of aliphatic polyethers, aliphatic polyesters, polyethers having a main chain that is semi-aromatic and polyesters having a main chain that is semi-aromatic; and the bond between the elastomer and coloured coating results from interaction of the polyurethane and polar functions on the elastomer. In fact, said composition is laid on the vulcanized tire after treatment of the tire surface to provide reactive polar functions. The abovementioned coloured coating is said to inhibit the degradation due to oxidation and ozone and greatly limits the migration of the antioxidants towards the surface of the tire, allowing the rubber composition to retain its colour. Furthermore, the coating prevents the migration of the waxes towards the surface by a barrier effect, thereby avoiding efflorescence and retaining its surface appearance.
According to the Applicant, the compositions described above may show some disadvantages.
For example, the Applicant has noticed that the application of liquid polyurethane reaction mixtures (i.e., a liquid reaction mixture comprising an organic polyisocyanate and a polymeric material containing reactive hydrogen atoms) to the surface of the vulcanized tires which has to be coated, may cause release of carbon dioxide which may lead to the formation of defects on the coated surface with a consequent poor appearance of the same. On the other end, the Applicant has noticed that the use of compositions comprising polyurethanes may show discoloration problems due to the surface migration of antioxidants, antiozonants and waxes usually present in the elastomeric compositions, in particular in those used in tires manufacturing. Moreover, difficulties have been encountered in obtaining a good adhesion between compositions comprising polyurethanes and the surface of the vulcanized tires to be coated.